Unified head for a stacked fastener

ABSTRACT

A unified head for a staked fastener wherein the unified head is made from a first member in combination with a supplemental member, and the two members have at least one shared fiber. In a staking operation that forms the unified head, the operation is conducted in such a manner that a portion of a fiber, initially within the first member or the supplemental member, crosses the boundary therebetween creating the shared fiber, i.e., a segment of a single fiber is embedded in the first member and a segment is embedded in the supplemental member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/012,595 entitled “Unified Head For a Staked Fastener,” filed on Feb.4, 2008 which is a divisional of U.S. application Ser. No. 10/955,174,filed on Sep. 30, 2004, now U.S. Pat. No. 7,351,022. The entiredisclosure of these applications is hereby incorporated in its entiretyby reference.

FIELD OF THE INVENTION

The present invention relates to fasteners and more specifically tofasteners formed by staking, such as studs and rivets.

BACKGROUND

Staked fasteners, such as studs and rivets, are a well-known fasteningtechnology. Studs are typically used to secure a body, such as a circuitboard, to a foundation. Rivets, on the other hand, are typically used tofasten two bodies, such as sheet materials, together at an overlappingseam. For either a stud or a rivet, fastening is accomplished by thecreation of a head on a shank. In the case of a stud having two ends, ahead is formed on one end of the shank with the other end fixed to thefoundation with the body therebetween. In the case of a rivet, heads areformed on both ends of the shank with the bodies therebetween.

A staked fastener can be made from many materials, such as steel,aluminum and plastic. Where weight is a concern, such as in an airplane,helicopter, or spacecraft, materials with high strength-to-weightratios, such as plastic, are preferred. Unfortunately, plastic rivetssimply do not have the ultimate strength of rivets made from othermaterials. As a result, plastic rivets, though desirable for manyapplications, cannot be practicably used, or in some cases used at all.

There have been many advances in the plastic rivet. From an initialbeginning when plastic rivets were simply all plastic, such as athermoplastic (e.g., polyetheretherketone (more commonly known as“PEEK”)), newer composite plastic rivets have some type of reinforcementadded to the plastic. For example, many composite plastic rivets arereinforced with fibers, such as carbon or glass.

Rivets are typically formed in a two step process. First, an initialhead is formed with a shank extending therefrom. Generally, the initialhead is formed in a factory setting by a machine, by molding or stakingan end of a rod, which tends to make a high quality initial head with aproperly contoured contact surface (the surface of the head that willabut the body). Also, additional fabrication of the initial head, suchas cleanup of the contact surface, can be performed relatively easily.

Then in an application, a second head is formed in situate on the end ofthe shank. More specifically, when a rivet is used in an application,such as connecting two bodies, a hole is made in each of the two bodies.The diameter of the holes is sized such that when the holes are alignedwith each other the shank can pass through, but the initial head can notpass through the first hole that the shank passed through. The secondhead is then formed on the other end of the shank, thereby securing thetwo bodies together.

Unlike the initial head, the second head is formed at the job site,typically using a hand held tool, thus the conditions are not ascontrolled as those during the formation of the initial head.Additionally, cleanup of its contact surface is impossible, as it isabutting the body. As a result, the precision of the contact surface ofthe second head is generally not to the level of that of the contactsurface of the initial head. This discrepancy results in a second headwith less strength than the initial head.

More specifically, many processes used on plastic rivets to form thesecond head create voids in the contact surface of the rivet head. As aresult, the head has a local weakness at its parameter edge. If pressureis applied thereto, it will cause a local failure of the head. Theselocal failures result in “play” between the rivet and body, therebycreating the unacceptable amount of movement between the head and theshaft, causing the rivet to fail.

What is needed in the art is a staked fastener head and way to make thehead such that the resulting rivet, or stud, is stronger than itotherwise would be.

SUMMARY OF THE INVENTION

This invention is a unified head and a method for making it for a stakedfastener, such as a rivet. In an exemplary embodiment of a rivetemploying the unified head, a shank with two ends has an initial headformed at one end. Proximate the other end is at least one fiberembedded in the shank. In an application, the shank is passed through abody and a unified head is formed by staking the shank's other end,thereby trapping the body between the heads. In forming the unifiedhead, a first member is created from a clinch portion of the shank(which has at least a portion of the at least one fiber therein), and asupplemental member placed proximate the first member such that thesupplemental member is trapped during staking between the forming firstmember and the body. Additional sufficient energy is applied duringstaking such that at least one of the at least one fibers will become ashared fiber (a fiber having one segment embedded in the supplementalmember and another segment embedded in the first member).

These and other features, aspects, and advantages of embodiments of thepresent invention will become apparent with reference to the followingdescription in conjunction with the accompanying drawings. It is to beunderstood, however, that the drawings are designed solely for thepurposes of illustration and not as a definition of the limits of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of a rivet connecting two bodies having aunified head of the present invention.

FIG. 2 is a series of three drawings, individually identified as A, B,and C, each taken along cross-section 2-2 of FIG. 1, showing thecreation of a unified head of the present invention.

FIG. 3 shows a perspective view of a style of supplemental member foruse in the present invention.

FIG. 4 shows a perspective view of another style of supplemental memberfor use in the present invention.

FIG. 5 is a cross-sectional view of the supplemental member shown inFIG. 4 taken along line 5-5.

FIG. 6 is a perspective view of another style of supplemental member foruse in the present invention.

FIG. 7 is a side view of the supplemental member depicted in FIG. 6.

FIG. 8 is a cross-sectional view of the supplemental member depicted inFIG. 6 used in an application.

FIG. 9 is an expanded perspective view of another embodiment of asupplemental member.

FIG. 10 is an expanded perspective view of another embodiment of asupplemental member.

FIG. 11 is a side view of another embodiment of a supplemental member.

FIG. 12 is a side view of the supplemental member depicted in FIG. 11having another orientation.

FIG. 13 is yet another style of supplemental member for use in thepresent invention.

FIG. 14 is a cross-sectional side view of another shape of a firstmember of the present invention.

FIG. 15 is a top view of the first member depicted in FIG. 14.

FIG. 16 is a cross-sectional view of a stud employing a supplementalmember.

DETAILED DESCRIPTION

Referring to FIG. 1, a rivet, generally referred to by reference number10, secures a first body 12, such as a sheet material, to a second body14, such as a sheet material. The rivet 10 has an initial head 16 havinga contact surface 18, a unified head (generally referred to by referencenumber 20) having a contact surface 22, and a grip member 24. Theunified head 20 has a first member 26, which is formed from a clinchportion 28, and a supplemental member (not easily seen in this view,discussed below).

The grip member 24 and the clinch portion 28 are separate segments of ashank 30, which extends outwardly from the initial head 16. In theembodiment depicted in FIG. 1, the grip member 24 is that segment of theshank 30 passing through holes 32, 34, which are defined by the firstand second bodies 12, 14. The clinch portion 28 (depicted by dottedlines) is the segment of the shank 30 extending outwardly beyond asurface 35 of the second body 14. As those skilled in the art willappreciate, the precise demarcation between the grip member 24 and theclinch portion 28 of the shank 30 is a function of the style of head(flush, as shown, or countersunk), which determines the contact surfaceof the head. Thus, the demarcation point should not be strictlyconstrued to begin at the surface of the body from which the shankextends, as shown in this exemplary embodiment. Additionally, the use ofadditional elements, such as washers, may alter the demarcation point.Also, it should be appreciated that the initial head 16 could be formedfrom another clinch portion of a rod (not shown), thereby creating theshank 30 with the initial head 16. It should also be appreciated thatthe initial head 16 could be of the same structure as the unified head20.

Referring to the series of Figures that comprise FIG. 2, the rivet 10has the unified head 20 formed in the following manner. As shown in FIG.2A, the rivet 10 originally has the initial head 16 and the shank 30,with the grip member 24 and the clinch portion 28, which has an end 36.An enlarged view of the clinch portion 28 of FIG. 2A, shows at least onefiber 38 contained therein. The at least one fiber 38 in the clinchportion 28 is oriented generally parallel to the centerline of the shank30.

A supplemental member 40 is collocated with the clinch portion 28 of theshank 30 proximate the second body 14. Further discussion of thesupplemental member 40 is presented below.

Continuing with FIGS. 2B and 2C, the first member 26 is formed bystaking the end 36 of the clinch portion 28 with a staking tool (notshown). The staking operation continues over a distance d_(s) until theunified head 20 is formed.

As shown in the expanded view of FIG. 2B, the staking operation, whichmay utilize a staking tool, such as one having a semi-hemisphericalshape (not shown), tends to bend the at least one fiber 38 in the firstmember 26 toward a perimeter segment 42, which will eventually abut thesupplemental member 40. A void 44 defined by the perimeter segment 42 ofthe first member 26 may be formed during the staking operation.

As shown in FIGS. 2B and 2C, the staking operation brings the firstmember 26 into contact with the supplemental member 40. The energy fromthe staking operation enters the supplemental member 40 causing it todeform to the contour of the perimeter segment 42, entering the void,and forming at least part of the contact surface 22 of the unified head20.

The staking procedure imparts to at least one of the at least one fibers38 and the supplemental member 40 sufficient energy such that a portionof those fibers cross the boundary and become embedded in thesupplemental member 40. As a result, at least one of the at least onefibers 38 will become a shared fiber 45. The shared fiber 45 being afiber that is simultaneously embedded in the first member 26 and thesupplemental member 40. In other words, the shared fiber 45 will have asegment embedded in the first member 26 and a segment embedded the insupplemental member 40. As shown in FIG. 2C in the expanded view, ashared fiber 45 a could cross the perimeter segment 42 more than once.

The staking method employed depends upon the materials selected for theclinch portion 28 and the supplemental member 40. For example, where theclinch portion 28 and the supplemental member 40 are plastic, suchmethods as ultrasonic and/or induction could be used.

The staking procedure to create a shared fiber 45, however, is differentthan conventional procedures. In a standard ultrasonic procedure, thestaking procedure is controlled by the distance d_(s) the staking toolmust travel to accomplish the formation of the relevant head. Morespecifically, sufficient energy is applied to the clinch portion 30 viathe staking tool to cause the clinch portion to flow thereby allowingthe staking tool to act on the clinch portion to travel the distanced_(s) to deform the clinch portion into a desired head shape. Once thedesired head shape is accomplished, i.e., the travel distance d_(s) hasbeen accomplished, the energy is removed, but the staking tool is heldin position for some hold time. The hold time allows the head, which isunder the staking tool and still fluid enough to flow, to coolsufficiently so that the staking tool can be removed without the clinchportion further flowing. In the procedure of the invention, there is afixer step in the staking procedure that occurs after the traveldistance d_(s) has been accomplished prior to the hold. In the fixerstep, energy is still applied, generally at the level previously used,to the pre-head (the head as it exists immediately after the traveldistance d_(s) has been reached). The fixer step adds additional energyto the pre-head to create the shared fiber 45, thereby converting thepre-head to a unified head 20. The amount of energy is applicationdependent depending on such factors as the materials used in thepre-head and their associated masses. Depending upon the degree ofadditional energy added during the fixer step and the materials used,the supplemental member 40 and the first member 26 may merely be weldedto each other or may form a coherent mass.

If induction staking is used, materials that generate heat when exposedto induction energy would most likely have to be present in the clinchportion 30, but could be present elsewhere, such as in the supplementalmember 40.

The supplemental member 40 can be of almost any shape, such as arectangular solid (FIG. 3), a washer (FIG. 4), a keyed structure (FIG.6), or a graduated structure (FIG. 11). Typically these types ofstructures have a hole 46, 48, 50 and 71, which is defined by thesupplemental member 40, sized to allow the clinch portion 28 of theshank 30 to pass through.

The supplemental member 40 should have a sufficient initial volume V1,V2, V3, V4 to permit it to at least fill the void 44. The supplementalmember 40 may have a greater volume than that necessary to fill the void44 that will simply flow out during the staking operation. As thoseskilled in the art will appreciate, some material of the first member 16may also flow out from under the staking tool as it travels the distanced_(s), causing a decrease in the density of the first member 16.Therefore, the volume V1, V2, V3, V4 of the supplemental member 40 maybe sufficiently increased above that required to fill the void 44 tocompensate for this loss in density.

As depicted in FIG. 5, at least one fiber 54 could be incorporated inthe supplemental member 40. It is, therefore, within the scope of theinvention if at least one of the at least one fibers 54 from thesupplemental member 40 becomes a shared fiber 45 regardless of whetherthe clinch portion 28 of the shank 30 has fibers or not.

Referring to FIGS. 6, 7, 8, 9 and 10, the supplemental member 40 may bea keyed structure. As shown in FIGS. 6 and 7, a supplemental member 40has a keyed structure of a top-hat design having a brim 56 with a crown58 extending therefrom. In one application, the crown 58 is insertedinto the hole 34 of the second body 14, and the shank 30 of the rivet 10is inserted through the hole 54 such that the clinch portion 28 extendsoutwardly from the brim 56. As shown in FIG. 8, in a keyed structure, aportion, i.e., a key, of the supplemental member 40, such as the crown58, can be positioned between the grip member 24 of the shank 30 and thesecond body 14 and even into the first body 12.

The keyed structure may also have the additional feature of anon-rotational cross-sectional shape such that in cooperation with thecross-sectional shape of the hole the supplemental material will notrotate within the hole defined by the body, or bodies. For examplereferring to FIGS. 9 and 10, the hole 34 and the supplemental member 40could have a crown 58 with a complementary rectangular cross-sections,or a corresponding protrusion 62 and slot 64.

The supplemental member 40 may also be graduated. Referring to FIG. 11,an example of a graduated design for a supplemental member 40 in theform of a top-hat having a brim 66 and a crown 68. In application, thecrown 68 would most likely extend outwardly from the surface 35; howeveras shown in FIG. 10 the graduated member could have the oppositeorientation. Depending upon the application, other graduated shapes,such as frustum of pyramid, could be used.

The supplemental member 40 may also be designed to engage the clinchportion. Engagement could be by friction or mechanical fastener. Asshown in FIG. 12, the fastener could be grips 70 for engaging the clinchportion 28 extending outwardly from a surface 72 that defines the hole71. The fastener could be of a one-way design, i.e., the fastener isbroken to effectuate removal of the supplemental member 40.

Referring to FIG. 13, the supplemental member 40 could also be a wrap60, such as a cord or tape, applied around the rivet 10, most likely thegrip member 28 proximate the second body 14. The cross-section of thewrap 60 could be any shape.

While the results of a hemispherical shaped head for a staking tool havebeen previously depicted, other shapes can be used. FIGS. 14 and 15depict a symmetrical unified head 20. The symmetrical head 20 has afirst member 26 where the at least one fibers 38 generally extendradially from the centerline of the clinch portion 28. This symmetry isaccomplished by using a staking tool 74 with a shank center locator 76.The shank center locator 76 penetrates into the clinch portion 28 of theshank 30 on the longitudinal axis causing the at least one fibers 38 tobe splayed radially outwardly therefrom.

Materials for the rivet 10 and supplemental member 40 are a matter ofdesign choice. Typical plastics, which include thermoplastics, such asPEEK or polyetherimide (more commonly known as PEI), are particularlywell suited for the invention. As discussed above, staking may cause aweld to occur between the material of the rivet 10 and the supplementalmember 40 and even between the rivet and/or the supplemental member andthe second body 14.

As those skilled in the art will appreciate, the strength of the weld orwhether a coherent mass is formed between the first member 26 andsupplemental member 40 is, among other things, dependent upon thematerials from which the rivet and supplemental member are made. If therivet and supplemental member are made from compatible or the samematerial, the weld could be stronger and the coherent mass more uniformthan it might otherwise be.

Any fibers can be embedded into the plastic of the rivet 10 orsupplemental member 40. Fibers are also a matter of design choice andmay include carbon or glass. Carbon fibers are particularly strong andlightweight.

The at least one fiber 38 in the shank 30 has been depicted in FIG. 2 asbeing oriented generally parallel with the centerline of the shank 30,but the at least one fibers could have any orientation. Where there aretwo or more fibers 38 in the shank 30, they could be randomly orientedone to the other. Additionally, the at least one fibers 38 can be of anylength, even running from end to end through the grip portion and clinchportions of a rod (not shown) from which the rivet 10 was created. Alsoin the case of multiple fibers 38, fibers of varying lengths could beused. Therefore, depending upon the length of the particular fibers inthe first member 26, a majority of the length of the shared fiber 45could be in the first member, or in the supplemental member 40. This isequally true for the at least one fibers 54 incorporated in thesupplemental member 40.

Referring to FIG. 2, a filler 78 maybe added about the grip member 24between the two bodies 12, 14. The filler 78 can be of any shape, suchas a washer, and be made from any number of materials to meet anyparticular need. For example, the filler 78 could contain a rubber orneoprene to provide a seal, or an adhesive, such as a 100% solidsadhesive, that would be activated, in the case of a 100% solids adhesivemelt and flow, as a result of the staking operation for providingadditional bonding between the first and second bodies 12, 14.

Referring to FIG. 16, in the case of a stud 80 having one end affixed toa foundation 82, it would be beneficial to create a stop 84 to supportthe filler 78. The stop 72 could be created in any number of ways suchas by a notch in or taper of the shank 30.

While there has been illustrated and described what is at presentconsidered to be preferred and alternative embodiments of the claimedinvention, it will be appreciated that numerous changes andmodifications are likely to occur to those skilled in the art. Forexample, while the unified head has been shown for a rivet, it isequally applicable for use with a stud. In addition, the unified headcould be used for both heads of a rivet. Also, the use of the singularshould be interpreted to mean at least one unless the specificationmakes such expressly clear. It is intended in the appended claims tocover all those changes and modifications that fall within the spiritand scope of the claimed invention.

1. A method of making a rivet: providing a shank having an initial head,passing the shank through a body, thereby defining on the shank agripping portion and a clinching portion, placing a supplemental memberhaving at least one fiber therein proximate the clinching portion andthe body, and staking the clinching portion and the supplemental membercreating a unified head.
 2. A method of staking a clinch portion of afastener comprising the steps of: providing a clinch portion, providinga supplemental member, staking the clinch portion into the supplementalmember creating a pre-head, wherein the staking includes a fixing step.3. The method of claim 2 wherein in the step of staking, the fixingemploys an ultrasonic method.